This invention relates to an apparatus for securing a part, such as a work holder or fixture, capable of monitoring, sensing, or measuring the mechanical distortion of the part as it is machined, treated or otherwise operated upon.
It is well known that metallic parts, such as aircraft engine parts, may distort when subjected to processes such as burnishing, shot peening, laser shock peening, or other similar treatments. These distortions are caused by compressive stresses that are introduced and tensile stresses that develop in the part as a result of such processes. A part may be subjected to processes such as burnishing, shot peening or laser shock peening to improve the parts resistance to stress related failure mechanisms. The benefit of such processes is obtained by inducing compressive stresses in the surface of the part. Metallic materials treated in such a manner respond to the introduction of compressive stresses by being self-equilibrating. Thus, as compressive stresses are introduced in the part, reacting tensile stresses form elsewhere in the part such that all forces within the volume of the part sum to zero. However, as these stresses develop, the material forming the part may react by distorting to accommodate the introduction of new stresses.
One problem associated with such distortions is that they go beyond the acceptable engineering tolerances for that particular part. While the mechanisms that cause distortion are known and understood, monitoring individual parts for excessive distortion beyond acceptable engineering tolerances has been difficult because of the various factors that contribute to distortion as well as the complexity of many part designs. Factors that have been found to contribute to distortion include the type, magnitude and pattern of stress introduced in the part, the particular method by which the part was treated, the material(s) from which the part is made, and the particular geometry of the part. Another substantial factor which impacts distortion are variations in individual parts, most notably in parts being treated that have already undergone some service life and are being remanufactured or refurbished. Under such circumstances, it becomes even more critical to monitor the response of each individual part to the treatment process for quality control purposes. Furthermore, for parts having complex geometries, such as gas turbine engine blades, it is difficult to measure the degree to which the part may have distorted, especially in the context of a sizeable manufacturing operation.
Accordingly, until now, it has been impractical or unduly laborious to measure individual parts and thereby assess whether a part has been adequately processed or whether a particular treatment operation has caused distortion beyond acceptable engineering tolerances. Therefore, a need exists for a relatively inexpensive method and apparatus for determining the distortion of a part as a result of a treatment process and that is easily implemented in a manufacturing environment.